Analysis of Fracture Reasons for an HL Grade 35CrMo Sucker Rod

The properties of a sucker rod material were tested by means of chemical composition analysis, metallographic examination and mechanical property testing. The morphology of fracture and corrosion products on the fracture surface were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) respectively. The resistance to hydrogen sulfide stress corrosion cracking for the sucker rod material was evaluated by hydrogen sulfide stress corrosion test. The results show that the chemical composition and tensile properties of the failed sucker rod met the requirements of relevant standards. Fracture surface could be divided into two regions with completely different characteristics. One of the areas had a smooth fracture, a black surface and obvious corrosion products. In the other area, there was a shear lip, no obvious plastic deformation, no obvious corrosion products on the surface, which displayed a typical fatigue fracture. After the hydrogen sulfide stress corrosion test, the sucker rod samples all broke. The sucker rod had poor resistance to hydrogen sulfide stress corrosion cracking. The main reasons for the fracture of the sucker rod were the stress corrosion cracking caused by hydrogen sulfide stress corrosion cracking in the early stage, which led to the stress concentration and the fatigue fracture under the alternating load in the final stage.